Drilling systems are frequently used to provide cylindrical holes in metallic work pieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tailstock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring application by simply changing the insert and not the entire drill assembly.
For many applications, it may be desirable to form a hole in a work piece which terminates in a flat bottom surface. In general, the drilling system as described above may utilize one type of drill insert for starting such a hole, and then using an insert to produce the desired flat bottom in the hole. Prior cutting inserts that were designed to cut flat bottomed holes have various deficiencies. For example, one type of these inserts had cutting edges extending from a center portion that were opposingly angled planes, with the center portion being removed in order to accommodate the cutting surfaces to cut a flat bottomed hole. The removal of this center area created a weakened area, point or line where the prior art inserts would occasionally break or fracture. Also, prior art flat bottom hole cutting inserts were designed with an imbalanced geometry causing it to wobble while drilling. This wobble or instability can cause deviations in the dimensions of the hole being bored, also known as runout, which is undesirable. Additionally, prior art drill systems and inserts were configured such that chips from the drilling process were not formed efficiently, causing deterioration of the cutting surfaces. The configuration of the cutting surfaces also did not allow for producing positive rakes in association with chip removal flutes to facilitate chip formation.